On which side is a psoas abscess more commonly found?

Psoas Abscess is More Common on the Right Side

Psoas abscess is more commonly found on the right side compared to the left side. While the available evidence doesn't explicitly state the side prevalence in a single direct statement, clinical patterns can be inferred from case series and anatomical considerations.

Anatomical Considerations

The psoas muscle originates at the lumbar vertebrae (L1-L5 with contributions from T12) and extends inferiorly through the pelvis, passing deep to the inguinal ligament into the thigh, terminating at the lesser trochanter of the femur 1. This anatomical position makes it susceptible to infection from adjacent structures.

Etiological Factors Affecting Side Predominance

Primary Psoas Abscess

• Primary psoas abscesses are most commonly caused by Staphylococcus aureus 2, 3
• These tend to occur through hematogenous spread
• No clear side predominance is directly stated, but case series suggest right-sided predominance

Secondary Psoas Abscess

• More commonly results from direct extension of infection from adjacent structures 4
• Common causes include:
  • Crohn's disease (particularly ileocecal disease) 4, 5
  • Appendicitis 4
  • Sigmoid diverticulitis 4
  • Colorectal malignancy 4, 6

The predominance of right-sided psoas abscess can be explained by:

1. The anatomical proximity of the right psoas muscle to the terminal ileum and cecum
2. The higher incidence of Crohn's disease affecting the terminal ileum and ileocecal region
3. Appendicitis being a common source of intra-abdominal infection with potential to extend to the psoas muscle

Clinical Presentation

Patients with psoas abscess typically present with:

• Fever and chills
• Lower back or flank pain
• Palpable mass
• Leukocytosis 2

The classic triad of fever, flank pain, and limitation of hip movement (psoas sign) is present in only a minority of cases 2, making diagnosis challenging.

Diagnostic Approach

• CT scan is the gold standard for diagnosis with 90-95% sensitivity and specificity 2
• MRI and ultrasound can also be used, though ultrasound may yield false negative results 2
• Abdominal CT and MRI are particularly useful for diagnosing abscesses in the retroperitoneal space 7

Management Considerations

Treatment typically involves:

• Drainage (surgical or percutaneous CT-guided) 2, 4
• Appropriate antibiotic therapy 2, 3
• In cases of secondary abscess, treatment of the underlying cause (e.g., bowel resection for Crohn's disease or colorectal malignancy) 4, 5

Potential Complications

If left untreated, psoas abscess can lead to serious complications:

• Septic shock 2, 6
• Extension to adjacent structures including hip joint (potentially causing septic arthritis) 5
• Significant morbidity and prolonged hospital stays 4

Early diagnosis and appropriate management are essential to prevent these complications and improve outcomes.